Cathode material for lithium ion secondary batteries, cathode member for lithium ion secondary batteries, lithium ion secondary battery, and method for producing cathode material for lithium ion secondary batteries

Abstract

A cathode material for a lithium ion secondary battery is a composite grain including an oxide and a carbon material. The oxide includes, as constituent elements, Li, Si and at least one of Fe and Mn. According to a measurement by an X-ray diffraction method using Cu-Kα as an X-ray source, a diffraction peak exists within a range of 2θ=33±2° and a half width of the diffraction peak is 0.55° or more. A size of the grain is 1 μm or more and 20 μm or less.

The invention claimed is: 
     
       1. A cathode material for a lithium ion secondary battery being a composite grain comprising: an oxide including, as constituent elements, Li, Si and at least one of Fe and Mn; and a carbon material, wherein
 according to a measurement by an X-ray diffraction method using Cu-Kα as an X-ray source, a diffraction peak exists within a range of 2θ=33±2° and a half width of the diffraction peak is 0.55° or more, 
 a size of the grain is 1 μm or more and 20 μm or less, and 
 a sea-islands structure is inside the grain in which the oxide is scattered as islands in a sea of the carbon material. 
 
     
     
       2. The cathode material for a lithium ion secondary battery according to  claim 1 , wherein a void having a size of 200 nm or more exists inside the grain. 
     
     
       3. The cathode material for a lithium ion secondary battery according to  claim 2 , wherein an abundance of the void is 20% or more and 80% or less in terms of an area rate in a section of the grain. 
     
     
       4. The cathode material for a lithium ion secondary battery according to  claim 1 , wherein an average circle-equivalent diameter of the islands of the sea-islands structure is 3 nm or more and 10 nm or less. 
     
     
       5. A cathode member for a lithium ion secondary battery, comprising a metal foil provided with a cathode layer including: the cathode material for a lithium ion secondary battery according to  claim 1 ; and a binder. 
     
     
       6. A lithium ion secondary battery comprising the cathode material for a lithium ion secondary battery according to  claim 1 . 
     
     
       7. A method for producing the cathode material for a lithium ion secondary battery according to  claim 1 , comprising:
 pyrolyzing a solution in a state of being liquid droplets, the solution including: a compound including elements composing an oxide including Li, Si and at least one of Fe and Mn as constituent elements; and an organic compound which produces a carbon material, to react the compounds with each other; and using a grain obtained through the reaction.